The present invention generally relates to fiber optic interferometer gyroscopes, and more particularly to a fiber optic gyroscope having improved readout and modulation index control.
Solid-state interferometer gyroscopes, including Sagnac interferometer gyroscopes which utilize the Sagnac effect, have been becoming of increased interest for widespread utilization in applications such as inertial navigation instruments, attitude and heading indicating or controlling devices, or the like. The Sagnac effect is a term in the electro-optics art describing a phase shift (and consequent measurable rotation rate) caused by nonreciprocity (different optical path lengths) of two counter rotating light waves traveling in the same coil in a fiber optic gyro or ring interferometer.
It was discovered that a convenient light path can be established with the use of an optical fiber formed in a coil or ring encircling an axis of rotational selectivity. Such a gyroscope is taught, for example, in U.S. Pat. No. 4,013,365.
It was later discovered that by modulating the light beams propagating in each counter-rotating direction with respective different frequencies, the signal processing thereof can be accomplished electronically with greater resolution and with a high degree of simplicity at lower, non-lightwave frequencies.
Fiber optic gyroscope apparatuses may serve as an angular speed and attitude detector in an inertial navigation apparatus for an aircraft or the like. Advanced fiber optic gyroscopes such as disclosed by U.S. Pat. No. 4,913,548 are capable of determining both the magnitude (and thereby also the rate) and the direction of rotation the optical fiber ring by examination of the differences in phase information between counter propagating beams in the fiber optic ring.